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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="checklist-modifiers"></a>Test for modifier keys correctly</h2></div></div></div>
<p><b>Why. </b>
        With <a class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="gtk_accelerator_get_default_mod_mask ()"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a> you can test for
        modifier keys reliably; this way your key event handlers will
        work correctly even if <span class="keycap"><strong>NumLock</strong></span> or
        <span class="keycap"><strong>CapsLock</strong></span> are activated.
      </p>
<p>
      In a <span class="structname">GdkEventKey</span>, the
      <em class="structfield"><code>state</code></em> field is a bit mask which
      indicates the modifier state at the time the key was pressed.
      Modifiers are keys like <span class="keycap"><strong>Control</strong></span> and
      <span class="keycap"><strong>NumLock</strong></span>.  When implementing a
      <a class="link" href="GtkWidget.html#GtkWidget-key-press-event" title="The “key-press-event” signal"><span class="type">“key-press-event”</span></a> handler, you should use
      <a class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="gtk_accelerator_get_default_mod_mask ()"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a> to
      test against modifier keys.  This function returns a bit mask
      which encompasses all the modifiers which the user may be
      actively pressing, such as <span class="keycap"><strong>Control</strong></span>,
      <span class="keycap"><strong>Shift</strong></span>, and <span class="keycap"><strong>Alt</strong></span>, but ignores
      "innocuous" modifiers such as <span class="keycap"><strong>NumLock</strong></span> and
      <span class="keycap"><strong>CapsLock</strong></span>.
    </p>
<p>
      Say you want to see if
      <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>F10</strong></span>
      was pressed.  Doing a simple test like
      <code class="literal">event-&gt;keysym == GDK_F10 &amp;&amp;
      event-&gt;state == GDK_CONTROL_MASK</code> is not
      enough.  If <span class="keycap"><strong>CapsLock</strong></span> is pressed, then
      <em class="structfield"><code>event-&gt;state</code></em> will be equal to
      <code class="literal">GDK_CONTROL_MASK | GDK_LOCK_MASK</code>, and the
      simple test will fail.  By taking the logical-and of
      <em class="structfield"><code>event-&gt;state</code></em> and
      <a class="link" href="gtk3-Keyboard-Accelerators.html#gtk-accelerator-get-default-mod-mask" title="gtk_accelerator_get_default_mod_mask ()"><code class="function">gtk_accelerator_get_default_mod_mask()</code></a>, you
      can ignore the modifiers which are not actively pressed by the
      user at the same time as the base key.
    </p>
<p>
      The following example correctly tests for
      <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>F10</strong></span>
      being pressed.
    </p>
<a name="default-mod-mask"></a><pre class="programlisting">
static gboolean
my_widget_key_press_event_handler (GtkWidget *widget, GdkEventKey *event)
{
  GdkModifierType modifiers;

  modifiers = gtk_accelerator_get_default_mod_mask ();

  if (event-&gt;keysym == GDK_F10
      &amp;&amp; (event-&gt;state &amp; modifiers) == GDK_CONTROL_MASK)
    {
      g_print ("Control-F10 was pressed\n");
      return TRUE;
    }

  return FALSE;
}
    </pre>
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